1. Field of the Invention
The present invention relates to an apparatus for receiving a digital television broadcast such as a digital ground wave broadcast or a digital cable broadcast, to a receiving apparatus capable of receiving both digital television broadcasts and current analog broadcasts, and to a receiving apparatus for receiving both digital and analog broadcasts.
2. Description of the Related Art
Digital broadcasting systems have been brought into use as television (TV) broadcasting systems following analog TV broadcasting systems.
A receiver for use in a digital broadcasting system such as a digital ground wave type broadcasting system or a digital cable type broadcasting system has a front end section, a transport section, an MPEG decoding section, a display processing section, and a control section. The front end section selects one of a plurality of carriers of electromagnetic waves received by an antenna, cancels ghost signals by using a digital filter (performs channel equalization), corrects errors, and outputs a transport stream. The transport section separates transport packets of the desired channel designated by a user from a plurality of channels multiplexed in the transport stream from the front end section, and descrambles the separated packets. The MPEG decoding section decodes MPEG-compressed video and audio signals in the desired channel transmitted through the medium of the transport packets output from the transport section to obtain video and audio outputs. The display processing section converts the MPEG-decoded images into a display format in accordance with the NTSC (National Television System Committee) system or the like. The control section is formed of a microcomputer or the like for controlling each section.
In the case of receiving an analog TV broadcast, a broadcast image can be immediately displayed on the screen of a display when a tuner selects the corresponding one of a plurality of carriers. Accordingly, in such receiving, the delay time between the moment at which a user inputs a command to change a channel and the moment at which an image and sound in a new channel are output depends only upon the time required for tuning in the tuner. In general, the time required for tuning in receivers for receiving analog TV broadcasts is about 200 to 300 msec. In analog TV broadcast receivers, no image is displayed for the time period corresponding to the delay time because only a distorted image can be displayed in the period corresponding to the delay time.
In the case of a receiving a digital TV broadcast, it is possible that about one second will be taken as a delay time between the moment at which a command to perform tuning for changing a channel is given and the moment at which an image appears on the screen of a display.
That is, for example, the time required for processing in the front end section, depending upon the number of taps of the digital filter for cancellation of ghost signals, is about 500 msec at the worst. A time of 100 msec is also required for MPEG decoding. Further, 30 msec is required for conversion of the MPEG-decoded output to a display format such as that in accordance with the NTSC system. The total delay time is the sum of these time periods and the tuner section processing time of about 200 to 300 msec.
To avoid display of a distorted image on the screen in the digital TV broadcast receiver, the method of displaying no image during the delay time may be used, as is in the conventional analog TV broadcast receiver. However, ordinary users, accustomed to the tuning speed of the existing analog TV broadcast receivers, are liable to feel that the above-mentioned delay in digital TV broadcast receivers is excessively long, and may be irritated when feeling a delay of display of a received image.
Moreover, many users expect the digital system to be higher in speed and quality than the analog system. For this reason, the above-described problem of a delay of receiving a digital TV broadcast is serious.
It is thought that analog broadcasting and digital TV broadcasting will coexist for a period of time, and that receivers capable of receiving both analog and digital TV broadcasts will be provided.
If so, and if it is impossible to immediately identify a channel designated by a channel selecting operation as an analog TV broadcasting channel or a digital TV broadcasting channel, a process is required in which tuning to the channel and reception of the channel are performed by each of analog and digital receiving sections to identify the channel. In such a case, however, the delay time before outputting an image and sound is further increased.
In view of the above-described circumstances, an object of the present invention is to provide a receiving apparatus and a receiving method arranged to reduce the delay time of tuning to and reception of a digital TV broadcast effectively and apparently.
To achieve the above-described object, according to a first aspect of the present invention, there is provided a television broadcast receiving apparatus comprising a tuner section for selecting one carrier from an input signal, a front end section for demodulating the carrier selected by the tuner section, the front end section having a channel equalizer formed of a digital filter, a transport section for separating a desired channel from a stream from the front end section, and for descrambling in the separated channel, a decoding section for decoding a signal in the separated desired channel to obtain at least one of an output video signal and an output audio signal, a display section for displaying an image based on the output video signal from the decoding section, a coefficient memory for storing equalizer coefficients to be supplied to the digital filter forming the channel equalizer, and control means for generating equalizer coefficients to be supplied to the channel equalizer by using the equalizer coefficients in the coefficient memory.
In this receiving apparatus, computation of equalizer coefficients, with which a longest processing delay is caused in the total processing delay of the front end section, which is particularly long, can be performed by using equalizer coefficients stored in the coefficient memory to increase the processing speed. The time period between the moment at which a user inputs a channel change command and the moment at which an image is thereafter output is thereby reduced.
In the above-described receiving apparatus, control means may update the equalizer coefficients stored in the coefficient memory by using the equalizer coefficients newly generated.
The equalizer coefficients in the coefficient memory are thereby updated to values closer to ideal values, thereby further increasing the equalizer coefficient computation speed.
The receiving apparatus may also have means for supplying a predetermined wait-time video signal to the display section for a time period before an output video signal is obtained from the decoding section.
According to this arrangement, a wait-time image, e.g., an image containing letters xe2x80x9cTuning . . . xe2x80x9d or the like is displayed instead of blanking the display before the received image is displayed, thereby relieving user""s irritation during the waiting time.
In the above-described receiving apparatus, an image for identification of the selected desired channel is displayed by the display section for a time period before the desired video output is obtained from the decoding section.
For example, a logotype or the like of a broadcasting selected by a user is displayed on the screen during the waiting time, thereby further relieving user""s irritation.
The above-described receiving apparatus may further have storage means for storing program information previously provided in the same channel as the above-mentioned desired channel, and the program information previously provided in the desired channel and read output from the storage means is displayed by the display section for a time period before the desired video output is obtained from the decoding section.
For example, in a case where a plurality of programs are broadcast in one digital television broadcasting channel, program information previously provided is displayed as a wait-time image. Considering that the probability of each of such previously provided programs being changed is ordinarily considered to be low, previously provided program information can be conveniently used as advance data for selecting programs according to user""s need after tuning to the corresponding channel.
According to a second aspect of the present invention, there is provided a television broadcast receiving apparatus comprising a first tuner section for receiving one of digital television broadcasts, the first tuner section selecting one carrier from an input signal, a digital demodulation processing section for obtaining an output video signal and an output audio signal by demodulating an output signal from the first tuner section, by separating a desired channel, and by performing decoding, a second tuner section for receiving one of analog television broadcasts, the second tuner section selecting one carrier from an input signal, an analog demodulation processing section for obtaining an output video signal and an output audio signal in a desired channel by demodulating an output signal from the second tuner section, changeover means for making a changeover between a state where an image display and an audio output are made as reception outputs from the output video signal and the output audio signal from the digital demodulation processing section, and a state where an image display and an audio output are made as reception outputs from the output video signal and the output audio signal from the analog demodulation processing section, a channel map memory for storing identification information for enabling each of channels selectable as a tuning target to be identified as a digital television broadcasting channel or an analog television broadcasting channel, and control means for making a determination as to whether a channel selected by a channel selecting operation performed by a user is a digital television broadcasting channel or an analog television broadcasting channel, for supplying a tuning control signal to the corresponding one of the first tuner section and the second tuner section, and for changing the changeover means, the control section making the determination by referring to the channel map memory when the user performs the channel selecting operation.
In the channel map memory of this receiving apparatus, information for enabling each channel to be identified as a digital television broadcasting channel or an analog television broadcasting channel is stored. When a user performs a channel selecting operation, a determination as to whether the selected channel is an analog television broadcasting channel or a digital television broadcasting channel is made by referring to the channel map memory. Then, a tuning control signal is supplied to the suitable one of the analog television broadcast tuner section and the digital television broadcast tuner section according to the result of the determination. Therefore, there is no need for temporarily performing tuning by each of the first and second tuner sections. The tuning speed can be increased by eliminating the time for this tuning.
The arrangement of the receiving apparatus according to the second aspect of the invention may be such that analog television broadcast signals and/or the digital television broadcast signals contain guide information for presenting to a viewer a present state of broadcasting of channel programs or a schedule of broadcasting of channel programs, the guide information including a marker bit for enabling each channel to be identified as an analog broadcasting channel or a digital broadcasting channel, and the apparatus further comprises means for extracting the guide information from the broadcast signal, and for storing, as the identification information in the channel map memory, the marker bit obtained from the extracted guide information.
According to this arrangement, marker bits contained in broadcast signals are stored in the channel map to enable each channel to be identified as a digital television broadcast signal or an analog television broadcast signal, thereby eliminating the need for a process in which each channel is previously received to be ascertained as a digital television broadcasting channel or an analog television broadcasting channel. Even if the channel assignment is changed, the identification information can be updated by using the guide information. Thus, correct information for enabling each channel to be identified as a digital television broadcasting channel or an analog television broadcasting channel can always be maintained.
The arrangement of the above-described receiving apparatus may also be such that, if a channel selected by a user is an analog television broadcasting channel, a control signal for selecting a carrier in the selected channel is supplied to the second tuner section, and a control signal for selecting a carrier of a digital television broadcast in a channel supposed by using the channel map memory to be next selected by the user in the vicinity of the presently received channel is supplied to the first tuner section.
If the presently received television broadcast is an analog television broadcast, preliminary reception of a channel supposed to be next selected by the first tuner for receiving digital television broadcasts is performed in the background. A digital television broadcasting channel to which one of the tuners other than that presently tuned to the analog television broadcast, i.e., the first tuner, is to be tuned can be easily found by using the identification information in the channel map memory.
Further, the arrangement of the above-described receiving apparatus may be such that, if a channel selected by a user is an analog television broadcasting channel, a control signal for selecting a carrier in the selected channel is supplied to the second tuner section, and a control signal for selecting a carrier of a digital television broadcast in a channel supposed by using the channel map memory to be next selected by the user is supplied to the first tuner section, and that, if a channel selected by a user is a digital television broadcasting channel, a control signal for selecting a carrier in the selected channel is supplied to the first tuner section, and a control signal for selecting a carrier of an analog television broadcast in a channel supposed by using the channel map memory to be next selected by the user in the vicinity of the presently received channel is supplied to the second tuner section.
If the presently received television broadcast is an analog television broadcast, preliminary reception of a channel supposed to be next selected by the first tuner for receiving digital television broadcasts is performed in the background. If the presently received television broadcast is a digital television broadcast, preliminary reception of a channel supposed to be next selected by the second tuner for receiving analog television broadcasts is performed in the background. If the channel preliminarily received in this manner is actually selected subsequently, the receiving apparatus is immediately set in the state of being tuned to the channel to obtain a video output and/or an audio output.
When this preliminary reception is performed in the background, a digital television broadcasting channel to which one of the tuners other than that presently tuned to the selected channel is to be tuned can be easily found by using the identification information in the channel map memory.
According to a third aspect of the present invention, there is provided a television broadcast receiving apparatus comprising a first tuner section for receiving one of digital television broadcasts, the first tuner section selecting one carrier from an input signal, a digital demodulation processing section for obtaining an output video signal and an output audio signal by demodulating an output signal from the first tuner section, by separating a desired channel, and by performing decoding, a second tuner section for receiving one of analog television broadcasts, the second tuner section selecting one carrier from an input signal, an analog demodulation processing section for obtaining an output video signal and an output audio signal in a desired channel by demodulating an output signal from the second tuner section, changeover means for making a changeover between a state where an image display and an audio output are made as reception outputs from the output video signal and the output audio signal from the digital demodulation processing section, and a state where an image display and an audio output are made as reception outputs from the output video signal and the output audio signal from the analog demodulation processing section, control means for changing the changeover means according to whether a channel selected in accordance with a tuning operation performed by a user is a digital television broadcasting channel or an analog television broadcasting channel, and preliminary reception means for supplying a signal for receiving a broadcast signal in a channel supposed to be next selected by the user in the vicinity of the presently received channel to one of the first and second tuner sections not receiving the broadcast signal from which an image display and audio output are made as reception outputs through the changeover means.
In this receiving apparatus, one of the tuners other than that presently tuned to the selected channel is in a state for preliminarily receiving another channel supposed to be next selected by the user. Therefore, if the preliminarily received channel is actually selected by the user, the receiving apparatus can output an image and a sound in a markedly short time.
The arrangement of the receiving apparatus according to the second or third aspect of the invention may be such that the digital demodulation processing section has a channel equalizer formed of a digital filter, and the apparatus further comprises a coefficient memory for storing equalizer coefficients to be supplied to the digital filter forming the channel equalizer, and control means for generating equalizer coefficients to be supplied to the channel equalizer by using the equalizer coefficients in the coefficient memory.
According to this arrangement, coefficients to be supplied to the channel equalizer are computed by using the equalizer coefficients stored in the coefficient memory. By this simplification of computation, the time required for processing in the digital demodulation processing section can be reduced.
The apparatus according to the third aspect of the invention may also comprise a channel map memory for storing identification information for enabling each of channels selectable as a tuning target to be identified as a digital television broadcasting channel or an analog television broadcasting channel. When a user performs a channel selecting operation, a determination is made by referring to the channel map memory as to whether a channel selected by the channel selecting operation is a digital television broadcasting channel or an analog television broadcasting channel.
According to this arrangement, by referring to the identification information stored in the channel map memory and used for identifying each channel as an analog or digital television broadcasting channel, a tuning control signal can be immediately supplied to a suitable one of the tuner section for receiving analog television broadcasts and the tuner section for receiving digital television broadcasts. Therefore, there is no need for temporarily performing tuning by each of the first and second tuner sections. The tuning speed can be increased by eliminating the time for this tuning.
The arrangement may also be such that, if a channel selected by a user is an analog television broadcasting channel, a control signal for selecting a carrier in the selected channel is supplied to the second tuner section, and a control signal for selecting a carrier of a digital television broadcast in a channel supposed by using the channel map memory to be next selected by the user in the vicinity of the presently received channel is supplied to the first tuner section.
If the presently received television broadcast is an analog television broadcast, preliminary reception of a channel supposed to be next selected by the first tuner for receiving digital television broadcasts is performed in the background. A digital television broadcasting channel to which one of the tuners other than that presently tuned to the analog television broadcast, i.e., the first tuner, is to be tuned can be easily found by using the identification information in the channel map memory.
Further, the arrangement may be such that, if a channel selected by a user is an analog television broadcasting channel, a control signal for selecting a carrier in the selected channel is supplied to the second tuner section, and a control signal for selecting a carrier of a digital television broadcast in a channel supposed by using the channel map memory to be next selected by the user is supplied to the first tuner section, and that, if the channel selected by the user is a digital television broadcasting channel, a control signal for selecting a carrier in the selected channel is supplied to the first tuner section, and a control signal for selecting a carrier of an analog television broadcast in a channel supposed by using the channel map memory to be next selected by the user in the vicinity of the presently received channel is supplied to the second tuner section.
If the presently received television broadcast is an analog television broadcast, preliminary reception of a channel supposed to be next selected by the first tuner for receiving digital television broadcasts is performed in the background. If the presently received television broadcast is a digital television broadcast, preliminary reception of a channel supposed to be next selected by the second tuner for receiving analog television broadcasts is performed in the background. If the channel preliminarily received in this manner is actually selected subsequently, the receiving apparatus is immediately set in the state of being tuned to the channel to obtain a video output and/or an audio output.
When this preliminary reception is performed in the background, a digital television broadcasting channel to which one of the tuners other than that presently tuned to the selected channel is to be tuned can be easily found by using the identification information in the channel map memory.